The present invention relates to a photographic film cassette, and more particularly to an improvement in the light-shielding capability of a film passageway of a film cassette.
Recently, as disclosed in U.S. Pat. Nos. 4,832,275 and 4,834,306, a photographic film cassette has been proposed in which rotation of a spool can advance a film leader of photographic film, e.g. negative film wound therein, to the outside of a cassette shell through a film passageway. When such a cassette is in an unused condition, no film protrudes outside of the cassette. If plush or light trapping fabric is used in a conventional manner to shield the film passageway from light, such plush is provided with densely planted long pile threads. Alternatively, it is necessary to provide the film passageway with a light-shielding construction.
Japanese Patent Laid-open Publication No. 60-211453 discloses a cassette with a film passageway shielded from light, in which a plurality of elastic ribs are formed on the inside walls of the film passageway along a widthwise direction of the film. These ribs serve to reinforce the inside walls of the film passageway so that it is possible to prevent the film from being subjected to light by deforming the inside walls of the film passageway. Further, two or three pairs of light-shielding elastic members are attached to the inside walls of the film passageway so that one lengthwise side (attached side) is attached, and the thickness decreases slightly along the direction from the attached side to a side (free side) opposite the attached side. The overall elasticity of the light-shielding members is utilized effectively based on the decrease in thickness, so that it is possible to bring the tips of the light-shielding members in contact together reliably after winding up the film.
In a magazine for containing a photosensitive material as disclosed in Japanese Patent Laid-open Publication No. 63-124050, a light-shielding elastic plate is provided in a film passageway of a magazine casing to cover the whole length of the film passageway. The smooth edge of the elastic plate, crooked in the shape of a letter J, presses the film against the plush when the film is fed. The light-shielding capacity thus is improved without being affected by a degree of precision in sizes or gaps.
In a photographic film magazine as disclosed in Japanese Patent Laid-open Publication No. 2-27334, light-shielding elastic members 71 and 72 are attached to parallel tongues 70a and 70b forming a film passage mouth 11, as illustrated in FIG. 18. Attached sides 71a and 72a of the light-shielding members 71 and 72 are attached so that opposite or free sides 7lb and 72b are kept in contact to close the film passage mouth 11.
In the cassette disclosed in U.S. Pat. Nos. 4,832,275 and 4,834,306, plush provided with long pile threads densely planted, causes considerable resistance against a film leader when the leader is advanced. The torque applied to the spool needs to be large, while possibly causing the film leader to jam.
The above-described light-shielding structures of the film passageway, though suitable for the magazine of a large size, are difficult to use for the film passageway of a 135-type film cassette with 35 mm photographic film wound in a roll. In the cassette disclosed in Japanese Patent Laid-open Publication No. 60-211453, gaps will be formed between lateral sides of the light-shielding members and the inside walls of the film passageway, thus adversely affecting light-shielding capacity. Supposedly, it also is difficult for the advancing film leader to push open the four or six light-shielding members which are disposed to lap one over another in the film passage mouth.
In the magazine disclosed in Japanese Patent Laid-open Publication No. 63-124050, gaps also might be formed between lateral sides of the light-shielding plate and the inside walls of the film passageway, while the light-shielding plate might be bent and upturned beyond the range of its elasticity and thus allow light to enter the magazine. The film leader advanced by the rotation of the spool might not be fed between the plush and the J-shaped tip of the light-shielding plate, as the tip is firmly pressed against the plush. This light-shielding plate cannot be applied to a self-advancing film cassette.
In the magazine disclosed in Japanese Patent Laid-open Publication No. 2-27334, the two light-shielding members need a large resilient force to keep their free sides in fight contact, because the film passage mouth is closed by the contact of the free sides. However, it is difficult to advance the film leader against the resilient force of the light-shielding members. When the film is protruded for a long time, the free sides will be irrecoverably deformed so as to be no longer in mutual contact after even rewinding the film, so that the light-shielding capacity decreases, no matter how high the resilient force is. Because the inside surfaces of the film passageway are parallel to each other, the possibly curled film leader might be stopped by the attaching side 72a of the light-shielding member 72, thus making impossible the full advance of the film leader.